New research gives women another good reason to get plenty of bone-strengthening calcium and vitamin D: The nutrients may reduce the risk of developing breast cancer.
A team of Harvard researchers reported this week that premenopausal women who get more calcium and vitamin D -- either from food or supplements -- are less likely to get breast cancer.
Only about 20 percent of breast cancer cases occur in women younger than 50, but is often more aggressive. Mammograms, X-rays intended to find breast cancer earlier, are less accurate for women in their 40s and generally are not recommended for those younger than 40.
Though postmenopausal women can take medication to reduce their risk of developing breast cancer, nothing is available for their premenopausal sisters.
Although the evidence is not strong enough to advise all women to take calcium and vitamin D, experts say it might help reduce the risk of breast cancer and it's not likely to hurt.
"It's probably reasonable to consider," said Dr. Leslie Laufman, an editor of the National Cancer Institute's screening and prevention Web site. "There's no proof that making a change [in intake of calcium and vitamin D] matters -- but it probably does."
Other researchers called the findings "striking."
"There is no known way to reduce [the incidence of] premenopausal breast cancer, and this is a major finding," said Frank Garland, an epidemiologist.
"We think this is the most important development in the prevention of premenopausal breast cancer in history," said Cedric Garland, an expert in preventive medicine.
The Garland brothers and Edward Gorham, collaborators in the field of cancer prevention at the University of California-San Diego, proposed in 1989 that vitamin D and calcium could prevent breast cancer.
Laufman cautioned that it's not possible to prove the supplements prevent breast cancer without doing a more rigorous trial.
Researchers would have to randomly select a large number of women to receive either a supplement or a matching dummy pill, Laufman said, and then follow up to see whether one group developed more breast cancer. (The women in the Harvard study were not randomized; so it's possible that whatever caused some of them to take dietary supplements also affected their chances of getting breast cancer.)
But "it's worth talking about," said Laufman. "We know that sunlight, which is essentially vitamin D, is actually good for you. People exposed to sunlight have a lower risk of prostate cancer, colon cancer and breast cancer."
The Harvard study, published in this week's issue of Archives of Internal Medicine, found that calcium and vitamin D reduced breast cancer risk significantly only in premenopausal women. There was no protection for postmenopausal women, except for those taking the highest doses of both calcium and vitamin D.
The researchers, led by Jennifer Lin, said a possible explanation for the difference might have to do with the interaction between calcium, vitamin D and certain growth factors.
Laboratory studies have found that calcium and vitamin D can stop breast cells from multiplying out of control when those cells contain high levels of insulinlike growth factors. In humans, growth-factor levels decline with age, so the interaction is likely to be stronger in younger women.
But the Garlands said the explanation could be simpler: The women in the Harvard study weren't getting enough vitamin D and calcium.
Postmenopausal women already are advised to take calcium and vitamin D supplements to protect their bones, and many doctors recommend that women start taking the supplements well before menopause.
"To get an effect, you need bigger doses," said Cedric Garland. He recommends that women get up to 2,000 international units a day of vitamin D(-3) (the only form found to be effective) orally plus an additional 1,500 units by exposing their skin to sunlight between five and 15 minutes a day.
Judy Peres writes for the Chicago Tribune.